(a) Field of the Invention
The present invention relates to a method and device for estimating a frequency offset in a communication system. More particularly, the present invention relates to a method and device for estimating a frequency offset in an orthogonal frequency division multiplexing access (OFDMA) system.
(b) Description of the Related Art
In a communication system using a plurality of orthogonal subcarriers such as the OFDMA system, interference between adjacent subcarriers are increased to substantially increase the bit error rate when the orthogonality is not maintained. The orthogonality in a downlink may be lost by the frequency offset that is generated when the frequencies between the carriers of a base station and a subscriber station are not synchronized. Therefore, methods for estimating the frequency offset have been proposed in order to compensate for the frequency offset.
One frequency offset estimating method is to use the characteristic in which a preamble is repeated in the time domain. The above-noted method is to estimate a start point by searching an interval in which preambles are repeated, correlate the repeated preambles, calculate a phase value, and estimate a frequency offset. However, the method is not applicable to the system that uses subcarriers having preambles that are used to identify cells and sectors and are different for respective sectors and that uses different codes. For example, an application of the above-noted method to the IEEE 802.16e based system may generate frequency offset estimation errors.